Yes — grapefruit is safe and vitamin-rich, but its strong acidity means small amounts, occasionally.
Keeper's noteOffer a small segment and let your bird decide; many find it too sour. A few times a week at most for the ones that like it.
What to watch out for with grapefruit
Grapefruit is non-toxic and packed with vitamins A and C, but it's both acidic and bitter, so most parrots take only a little, and a lot can irritate the gut. Unlike with some medications in humans, grapefruit's drug-interaction concern doesn't have an established parrot parallel — the practical limit here is simply the acid.
How to serve it
Peel and offer a small segment; remove seeds and pith.